Separating Coupled Responsibilities

Note that in Figure 8-3, I kept both responsibilities coupled in the ModemImplementation class. This is not desirable, but it may be necessary. There are often reasons, having to do with the details of the hardware or operating system, that force us to couple things that we'd rather not couple. However, by separating their interfaces, we have decoupled the concepts as far as the rest of the application is concerned.

We may view the ModemImplementation class as a kludge or a wart; however, note that all dependencies flow away from it. Nobody needs to depend on this class. Nobody except main needs to know that it exists. Thus, we've put the ugly bit behind a fence. Its ugliness need not leak out and pollute the rest of the application.